1. Technical Field
The present invention relates to hoisting and conveying machine building and more particularly it relates to conveyor rollers and a method of manufacture thereof.
2. Background Art
The conveyor rollers known in the prior art comprise a hollow cylindrical shell which has consecutively arranged tapered and cylindrical portions at both ends thereof. The cylindrical end portions serve as axle shafts for mounting the bearings (see, for example, FRG Pat. No. 2413270 published Jan. 9, 1975).
This roller is intended for special applications of conveyors, i.e. in furnaces which determines the peculiarities of its design. It is made of a tubular billet and all its component parts, i.e. the hollow cylindrical shell, tapered portions and cylindrical axle shafts are made as an integral unit. The roller walls in all cross sections have the same thickness which is equal to the thickness of the tubular billet. The transition from the cylindrical portion of the shell to the axle shafts via tapered portions permits the roller to pass through the furnace walls which increases the distance between the bearings. The interior space of the roller is open and not sealed which is required for cooling the roller.
Another widely known roller comprises a hollow cylindrical shell, end walls which are perpendicular to the shell, and axle shafts for mounting the bearings. The end walls mostly made of steel plate are inserted into the bores of the cylindrical shell which is made of a tubular billet and are connected to said shell by welding, rolling-in or by some other type of joint suitable for the purpose. Solid axle shafts are also connected to the end walls, usually by welding.
Such a roller is labour-consuming in manufacture, insufficiently reliable in service due to frequent failures of the joint between the hollow cylindrical shell and the end walls and between the end walls and the axle shafts. The end walls made of steel plate have the same thickness in all cross sections so that the construction is not uniform in strength. The initial thickness of the walls of the tubular billet for making the hollow cylindrical shell has to be increased for making the recesses to receive the end walls. All these factors increase the consumption of metal during roller manufacture, the weight of the rotating masses, and the consumption of power during conveyor operation. The manufacture of such rollers calls for a considerable stock of machine tools and, consequently, comparatively large production floor areas.
Known in the prior art is a method of manufacturing conveyor rollers by the consecutive rolling of the ends of a tubular billet heated to a forging temperature. In this rolling operation a bar with a thicker portion is inserted into the tubular billet in the zone of its heated ends and, when said thicker portion of the bar is wedged after forming the outside diameter in the beginning of the axle shaft, the bar is moved axially from the billet, thus drawing the axle shaft and simultaneously cooling it with, say, water (see USSR Author's Certificate No. 553780, Cl.B21D 41/02). The known method is adapted only for manufacturing elongated axle shafts whose walls are thinner than the wall of the billet.
Another prior art method of making rollers with an axle shaft by rolling consecutively the ends of the tubular billet heated to a forging temperature and rotated during rolling (see USSR Author's Certificate No. 339337, Cl. B21D 41/04). However, this method fails to produce rollers wherein the end walls and axle shafts are made integral with the cylindrical shell and wherein the thickness of the end walls varies, growing into the cylindrical shell in the direction from its periphery to the geometrical axis.